ABSTRACT The goal of the proposed investigations is to provide preclinical and clinical information on the bio- disposition, efficacy, and safety of bupropion sustained release (SR) as an aid for smoking cessation in pregnant women. The majority of women who are smokers and become pregnant are aware of the known risks but are unable to quit smoking due to the addictive nature of nicotine. Behavioral interventions have a modest, but consistent, beneficial effect on smoking cessation. However, it is least effective in heavier smokers. Alternatively, medications are safe and effective for smoking cessation in nonpregnant smokers, but they are not approved for pregnant patients because their safety and efficacy have not been established. Bupropion SR has been successfully used for smoking cessation in nonpregnant smokers, and its long- term safety profile has been shown. Therefore, we propose a prospective, placebo-controlled randomized clinical trial of bupropion SR for smoking cessation during pregnancy. Pregnancy-induced changes in maternal physiology and/or common single nucleotide polymorphisms (SNPs) in the gene encoding the hepatic enzyme CYP2B6 might alter the metabolism of bupropion during pregnancy and, consequently, its concentration in maternal circulation, affecting is efficacy. Moreover, recent investigations in our laboratory revealed that bupropion crosses the placenta from the maternal to the fetal circuit and is metabolized by the tissue's enzymes. Our data indicate, furthermore, that placental metabolizing enzymes (carbonyl reductases), as well as its efflux transporters P-glycoprotein (P-gp) and Breast Cancer Resistant Protein (BCRP), have an important role in regulating placental disposition of bupropion and, consequently, fetal exposure to the drug. The hypothesis for this investigation is that bupropion is a safe and effective medication that can aid in smoking cessation during pregnancy. To examine the preliminary efficacy and safety of bupropion SR, the following specific aims will be investigated: (1) Examine whether bupropion SR reduces nicotine withdrawal symptoms, increases quit rates, and has a favorable safety profile compared to placebo; (2) Determine the effect of pregnancy-induced changes on the pharmacokinetics (PK) of bupropion SR at different stages of gestation and postpartum in the same individual; (3) Determine the effect of common single nucleotide polymorphisms (SNPs) in the gene encoding CYP2B6 on its activity in the biotransformation of bupropion and on 7-day point prevalence abstinence rates in pregnancy; (4) Determine the effects of chronic exposure to bupropion SR on the expression and activity of the placental carbonyl reductases; (5) Determine the effects of chronic exposure to bupropion SR on the expression and activity of the placental efflux transporters P-gp and BCRP. In summary, The information obtained is necessary for evaluating bupropion as a potential medication for aiding in smoking cessation during pregnancy.